This invention relates to systems for pipe bursting and replacement.
A variety of systems are now known for the installation of underground pipes, particularly for the replacement of an existing deteriorated pipe. In one widely practiced method, a pneumatic impact boring tool is sent through the existing pipeline such that the head of the tool, which may be provided with blades that apply intense local pressure to the existing pipe, fractures or splits the existing pipe. See, for example, Streatfield et. al. U.S. Pat. Nos. 4,720,211, 4,738,565 and 4,505,302. A replacement pipe, typically made of plastic such as HDPE, can be drawn along behind the boring tool. This process has proven effective commercially because it bursts the old pipe and replaces it with a new pipe at the same time. However, the system relies on a pneumatic impact tool, which in turn requires an air compressor. Exhaust from the impact tool is vented into the interior of the replacement pipe, which is unacceptable for certain types of pipe installations, such as gas and water lines.
Directional drilling machines are less effective for pipe bursting, especially for hard to burst pipes like cast iron, because the steady pushing force of the drill string lacks the impact power of a pneumatic impact boring tool. Thus, in some instances, a directional borer or winch is used to pull a pneumatic impact tool through an existing pipeline in order to burst the existing pipe and pull in the replacement pipe. These alternatives are effective but require considerable equipment and manual labor.
Wentworth U.S. Pat. No. 5,782,311 describes a pipe bursting apparatus that uses a directional boring machine capable of simultaneously rotating and pulling a drill string and an impact tool connectable to the drill string. The impact tool includes a tubular housing ending in a front bursting head, an input shaft, bearings supporting the input shaft for rotation within the housing, a striker disposed for reciprocation within the housing to deliver impacts to a front anvil, and a drive mechanism for simultaneously pulling the impact tool forward in response to a pulling force on the input shaft and for reciprocating the striker to drive the tool forward by the action of cyclic impacts on the front anvil. The apparatus can carry out a pipe bursting operation in a manner that eliminates the need to use a separate pneumatic impact tool to burst the existing pipe. This impact mechanism is effective but has the disadvantage of creating torsion on the drill string which can accelerate wear of the drill string and boring machine.
A method for replacement of an existing pipeline according to the invention includes the steps of:
(a) forming a first access tunnel from a first location on the surface of the ground to a starting location of the pipeline;
(b) forming a second access tunnel from a second location on the surface of the ground to a finishing location of the pipeline;
(c) then inserting a drill string through the first access tunnel, then into the pipeline at the starting location, then through the inside of the pipeline to the finishing location, then out of the pipeline and back to the surface of the ground through the second access tunnel;
(d) then installing a pipe bursting device on the drill string, the device having a length of replacement pipe attached thereto;
(e) then pulling the drill string with pipe bursting device attached back through the second access tunnel and into the pipeline, thereby drawing the replacement pipe behind the pipe bursting device and widening the second access tunnel;
(f) then pulling the pipe bursting device through the existing pipeline to burst the existing pipeline and pull the replacement pipe in to replace the existing pipeline; and
(g) removing the pipe bursting device from the replacement pipe when the replacement pipe is fully installed; and
(h) removing the pipe bursting device and drill string from the ground.
The word xe2x80x9cthenxe2x80x9d is used to mean that the step is performed after the immediately preceding step. It will be appreciated from the detailed description that follows that steps such as (a) and (b) need not be performed in the order listed to be within the scope of the present invention.
The pipe bursting device preferably is an impactor that delivers cyclic impacts to aid in bursting the existing pipeline. The impactor includes a housing, a striker disposed within the housing and a mechanism for causing the striker to deliver impacts to the housing in response to rotation of the drill string. For purposes of the present invention, xe2x80x9cburstingxe2x80x9d includes shattering an existing pipe (such as one made of ceramic), slitting it and pushing the resulting pieces or strips aside to make room for the new pipe, or any other mechanical operation which destroys the original pipe. The pipe bursting device may also be an expander for widening an existing hole of a type known in the art, with or without an impact mechanism.
According to a preferred form of the method, steps (a)-(e) comprise drilling the first access tunnel with a directional boring machine using a drill string having a drill bit mounted thereon, such as either a bit for drilling in soil, rock, or both, removing the bit and then inserting the drill string through the existing pipeline from the starting location to the finishing location, and then if necessary replacing a drill bit on the drill string and drilling the second access tunnel. The second drill bit may be the same or different from the first. The drill bit is then replaced with the pipe bursting device, and pipe bursting device is pulled through the second access opening, thereby widening the second access opening, prior to pulling it through the existing pipeline.
Often the starting and finish locations will coincide with manholes or other existing structures, or with a hole dug from the service to provide access. In such a case, a preferred method of the invention contemplates drilling the first access tunnel with a directional boring machine using a drill string having a drill bit mounted thereon which drills a hole in a wall of the manhole or other similar structure, which manhole adjoins the starting location. The first and second access tunnels each define acute angles relative to the ground, e.g., a downward slope such as 30-60xc2x0, and the existing pipeline extends in a substantially horizontal direction. It is useful to place a deflection plate in a position within the hole at the starting location for contacting the drill string and deflecting it from its acute angle in the first access tunnel to the direction of the existing pipeline. Similarly in a second pit or manhole, a similar plate is positioned if needed to deflect the drill string upwardly.
According to a further aspect of the invention, the pipe bursting device is pulled without rotation in steps (e) and/or (f) in order to provide a more accurate bore. A sonde of a type well known on the art may be mounted on the pipe bursting head so that the actual depth and direction of the second access tunnel may be closely monitored (as where obstacles are nearby) or mapped.
The invention provides an impactor for use with a directional boring machine having a drill string connectable to the impactor for pulling the impactor through an existing pipeline. Rotation of the drill string is used to drive an internal striker that delivers impacts in the pulling direction to an impactor housing as the impactor housing tows a replacement pipe behind it. The impactor housing is free to move in response to impacts from the striker over a limited distance in the pulling direction independently of the replacement pipe and drill string.
In a preferred form, such an impactor for use with a directional boring machine having a drill string that pulls the impactor while rotating includes a rotary drive shaft connectable to a terminal end of the drill string, an impactor housing mounted on the drive shaft for lengthwise sliding movement thereon, a striker disposed in an internal chamber of the housing, and one or more springs biasing the striker to a forward position in the chamber. A tail assembly behind the housing includes a bearing whereby the rotary drive shaft can pull the tail assembly while rotating within the bearing structure, and suitable means for pulling a pipe to be installed behind the tail assembly. A cam and follower assembly cause rotation of the drive shaft inside the housing to alternately move the striker rearwardly, compressing the spring, and then forwardly under the force of the compressed spring to impact an interior surface of the housing, cause the housing to move forward relative to the drive shaft and tail assembly. The pulling force of the drill string causes the housing to resume its former position after impact. These and other aspects of the invention are described in the detailed description that follows.